The broad, long-term objectives of this proposal are to understand the molecular mechanisms that are responsible for loss of type I procollagen synthesis in chronologically aged and photoaged human skin. Type I collagen is the major structural protein in human skin and provides skin with strength and resiliency. Type I collagen is synthesized in a precursor form, type I procollagen, by fibroblasts that reside in skin connective tissue. As skin ages, as a consequence of either the passage of time, or chronic exposure to ultraviolet (UV) irradiation from the sun (photoaging), type I procollagen synthesis declines. This loss of type I procollagen is a major contributing factor to thinning and increased fragility of naturally aged skin, and the old wrinkled appearance of photoaged skin. The mechanism responsible for loss of type I procollagen production in naturally aged and photoaged human skin is not known. The major regulator of type I procollagen synthesis is the transforming growth factor-beta (TGF-B)ISmad pathway. Evidence indicates that TGF-B regulates procollagen production both directly and indirectly, via TGF-B-regulated connective tissue growth factor (CTGF). UV irradiation impairs the TGF-B/Smad pathway, and this impairment is associated with reduced CTGF expression and reduced type I procollagen synthesis in human skin in vivo and human skin fibroblasts in vitro. Inhibition of the TGF-13/Smad pathway by UV irradiation occurs primarily as a consequence of down-regulation of the TGF-B receptor type II. This proposal will test the hypothesis that the TGF-B/Smad pathway is impaired in naturally aged and photoaged human skin, and that this impairment contributes to loss of type I procollagen synthesis. The specific aims are: 1) characterize TGF-13/SMAD signaling pathway in chronologically aged versus young human skin in vivo, 2) characterize TGF-B/SMAD signaling pathway in photoaged versus non-photoaged human skin in vivo, 3) determine the mechanisms by which UV inhibits TGF-B type II receptor gene expression in human skin fibroblasts, and 4) determine the role of CTGF in reduced procollagen in aged and photoaged human skin and the mechanism by which CTGF regulates procollagen production in human skin fibroblasts. The information obtained from the proposed studies will provide important new insights into modalities for treatment and prevention of age-related loss of skin strength and resiliency.